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    • #56956

      My brake system is basically new professionally rebuilt servo, new master cylinder, rebuilt calipers, wheel cylinders and new rubber brake lines. The metal lines have been cleaned with the outside coated with clear paint. the problem I have is whenever I first get in the car the pedal needs to be pumped up before I have brakes. I am using silicone brake fluid with basically a new system and there are no leaks. Any ideas as to what the problem is?


      Jim k

    • #61357

      If you have NO fluid loss (i.e., your master cylinder reservoir remains up), then it could be some air in the system. Does the pedal stay firm after pumping it up? Myself, I don’t use silicone, just Castrol LMA, but have heard others comment about a "soft" initial pedal when using silicone. Maybe Tiger Tom could shed some engineering expertise on this. If you do have fluid loss, with no visual indications of leaks, I would point to the brake servo. Double check: have you inspected EVERY fitting connection/bleeder screw/rear of the master cylinder? Look under dash above the brake pedal. No leaks anywhere? Bleed the system again. Best I can offer — good luck. And let us know what you find!

    • #61358


        Be careful using silicone brake fluid it tends to cause issues with the brake light switch and i have heard sometimes with other areas of the system.

      • #61359

        there are no leaks in the system, this week I will be replacing 2 suspect brake lines connected to the servo I the servo out so many times the fittings are over worked. what I would like to do is get rid of the servo and install a dual outlet master cylinder, if I go larger with the master cylinder piston it should make getting rid of the servo less of a strain on my leg.

      • #61360

        I had not heard about the synthetic fluid causing brake light switch problems, but….

        I have been running synthetic fluid for two years with no apparent problems. Unfortunately, my new brake light switch only lasted 18 months. What does the synthetic fluid actually do to the switch and is there anything that can be done other than switching back Castrol or fabricating a pedal actuated switch?

        Also, I believe the trick to bypassing the booster is to go to a smaller diameter, not larger. I bought the CAT underbore master and ended up having to fabricate a new pushrod for it but it works quite well.

      • #61361

        I have been running sythenic since I first put the Lister clone on the road in 1997.Yes everything was new except for the brakelight switch.It lasted a year.Replaced with a new one and haven’t experienced any problem since.Might just have been the switch was old and just failed.
        It is important however that nothing of the old fluid remains in the system.This means blowing the lines absolutely clean or replacing them as I did.
        As I said eveything was new except the switch and once replaced there were no more problems.Does this mean there is a reaction with the mixed fluids? The answer is I really don’t know.
        A few people have gone to a pedal operated brake switch with great results.At this time I see no need to do so but who knows.

      • #61362

        I realized I was backwards with the diameter and I need to go with a smaller diameter master cylinder. the brake system was completely apart and cleaned the wheel cylinders and calipers were rebuilt all of the brake line were cleaned with brake clean and blown out with air so I don’t have a contamination problem. I rebuilt the servo (it was bypassed prior) and about the same time I installed it the master cylinder started going bad and I thought it was the servo so I bought a rebuilt unit on E-Bay and after installing it I had the same problem with the pedal going down so I installed a new master cylinder.

        Back to the original problem the brake pedal needs to be pumped up after the car has been sitting it was doing the same thing with the other servo I seems to get better after bleeding the system but comes back after a week. The brake fluid doesn’t go down. like I said I am going to replace the brake lines at the servo this week and blled the brakes again.


      • #61478

        It’s been my experience that you need to bleed the brakes vigorously on a girling servo equipped car. The servo has some nooks and crannies that like to trap air bubbles. This hefty pedal pumping is contrary to how silicone fluids like to be handled, but you need some fluid velocity to get that trapped air out of there.

        For my part – Castrol LMA with annual changes.

      • #61490

        Assuming no leaks and all new rubber in brake system, pedal should be rock hard w/o servo. With servo there will be a slight movement and pulse felt on pedal when initially depressed with engine idling.

        For occasional driving, I highly recommend silicone. All brake fluids present problems in our cars. There is no perfect fluid. Silicone, in my opinion is the lesser of all evils. I do not want to discuss fluids here.

        The issue is spongy pedal. Silicone fluid requires special care when installing and bleeding. Done properly, you will have no problems for a long, long time.

        The first thing NOT TO DO. is "bleed the brakes vigorously". It’s just the opposite. When bleed vigorously, the fluid, any fluid, will tend to cavitate when going through orifices or internal restrictions. This creates a momentary negative pressure on the fluid.
        With silicone, the problem is more acute in that the fluid vaporizes at a lower vapor pressure. That is, it turns into a gas, as in air bubbles in the line. The fact is there is residual gas (air) in fluids. That is why they tell you to keep the containers closed at all times. Anyway, If you still have spongy brakes. I’d begin by bleeding our all the fluid. Save it if still clean. It is possible to remove the gas from silicone or any fluid by placing it in a vacuum chamber and pulling the air out. Most owners don’t have access to this. So new fluid is the easy way to go. A pint to pint and half should be sufficient.

        So how to bleed. The simplest way if you have the time is to allow gravity do it for you.
        1. Close all bleeder screws except one, any one. This screw should be open about 1/4 turn with hose connected into a container.

        2. SLOWLY, pour fluid in reservoir. Do not allow bubbles to form.

        3. Watch fluid, if it does not go down, prime system by slowly pushing master cylinder (brake pedal) in all the way. VERY IMPORTANT, SLOWLY, VERY SLOWLY, allow pedal to return. About 5 seconds. Remember, you do not want to aggravate the fluid at this time. It may be necessary to do this a couple of cycles. If impatient, you can continue this process til fluid goes out the bleeder.

        4. Allow about one reservoir volume to gravity feed through bleeder screw. Assuming fluid is clean, recycle in to reservoir.

        5. Close first bleeder screw, repeat gravity feed for remaining three screws.

        Obviously the reservoir must be kept full all the time or you start the process all over again.

        I have found that I have less problems by being patient and using the gravity approach. There is a tendency when pumping the master cyl to go too fast.

        This entire process takes about an hour.

        Having a second operator open/close the bleeder screw while the master cyl is being pumped works against you with silicone, any fluid for that matter. Its just that Silicone is more vulnerable. With the screw closed, a vacuum is created in the brake line. The vacuum along with resident air is mixed with the fluid in the line because of turbulence while moving as the master cylinder piston is being returned to its parked position. Now you know why silicone can be spongy.

        Silicone does cause rubber bladders in the brake light switches to fail . Count on it. Adapt a mechanical switch to the brake pedal arm just like all new cars do.

      • #61491

        The WORST thing to do is use one of the those hand pump bleeders with Silicone fluid. It just makes it worse if you drag the fluid out of the wheel cylinders.

        The best thing to do is push the fluid thru just like Tiger Tom said. Slowly and gently.

      • #61493

        Silicon fluid is great stuff have used for many years, like Tom said do it right you will have know problems!! The only draw back I have had with Silicon fluid is, later down the road if you have to have any paint work done in and around these areas Look out for the BIG FISHEYE!! 8)

      • #61497

        But at least silicone does not eat away your paint. Regular dot 3 or 4 will peel off your paint rather quickly. I have been there and prefer silicone.

        My question is: can you change a system filled with dot 3or4 to silicone without dismantling and cleaning the whole system? Is there a way to flush out the dot 3 or 4?

      • #61501

        Flushing out the Dot 3 or 4 is a must when doing a Dot5 conversion. Use a mild but volatile solvent, like Xylene. Just blow it thru with lots of compressed air. And a rag in a jar to catch the waste.

        (Avoid open flames, and keep the spray away from the paint)

      • #61502

        what should you do if you don’t know whats currently in there and you just want to bleed the current setup and hence top it up a little.

        do you have to blow it out and use silicone?

      • #61503

        Its pretty easy to tell silicone from DOT 3 or 4. Silicone will be slick in your fingers, a blue/purple color, and have little odor. DOT3 and 4 stinks, is almost black when old, and feels like you really shouldn’t have stuck your fingers in it. It makes your fingers feel "squeaky" when you rub them together.

        Don’t mix silicone with DOT 3 and 4. Gotta clean the whole system out first.

      • #61504

        I just bought some Prestone synthetic Dot 4 brake fluid…the label claims it’s compatible with all other brake fluids. Anyone ever use this stuff, or is it best avoided?

      • #61675

        I haven’t used it.

        When my car was redone a couple of years ago they used Valvoline(?) synthetic in the car, but failed to rebuild the drums. I’ve flushed out about 5 bottles of Valvoline stuff to ensure that the system is wiped clean, and there are no air pockets.

        I’ve also had to bypass/remove the brake booster, but not due to brake problems really. I suspect that the intake manifold was ingesting brake fluid due to a leak in the servo. That’s a later fix…

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